1. Field of the Invention
The invention relates to a method for three-dimensional color printing and a three-dimensional color printing device.
2. Brief Description of the Related Art
Three-dimensional printing or 3D printing refers to processes for printing a 3D object which can be also refer to as printing object. Existing 3D printers can use a variety of printing materials, wherein only few materials can be combined simultaneously for printing a printing object. As a result, the color gamut of the said 3D printing device is restricted and corresponds to only a fraction of the color space as only a limited number of colors can be generated, in particular via subtractive or autotypical mixture.
Therefore, printing objects or parts thereof which have a color outside the color gamut of the 3D printing device result in a false color reproduction.
It is known to provide an arrangement of printing materials by using half-toning algorithms. The document “J. Morovic et al. “HANS A new color separation and half toning paradigm”, Color and Imaging conference, vol. 2010, no. 1, Society for Imaging Science and Technology, 2010 demonstrates that the color gamut volume depends on the half-toning algorithm.
Also known is to apply a chemical layer after printing is finished to enlarge a color gamut (see e.g. the document “S. Mourad et. al., “Doubling the color gamut volume of inkjet prints using simple-post processing” , Conference on Color and Graphics, Imaging, and Vision, vol. 2006, no. 1, Society for Imaging science and Technology, 2006”).
In so called powder-binder jetting systems, full-color objects can be printed. Corresponding 3D printers use an inkjet-based technology for coloring a base material (powder). Via a post-processing, e.g. an infiltration of epoxy or cyanoacrylate-based particles, the color space can be enlarged (see e.g. the document “M. Stanic et. al., “Color measurements of 3-dimensional ink-jet prints”, NIP and digital fabrication conference, vol. 2008, no. 2, Society for Imaging science and Technology, 2008”).
Further known is 3D printing by a method referred to as polyjetting or multi-jet modeling. Herein, multiple printing materials are combined. UV-hardening printing inks are deposited and hardened slice by slice. Actual 3D printers, however, can combine only a limited numbers of printing materials, e.g. only up to three printing materials.
It is further known to use support material within the 3D printing process. The support material is a material which is regularly used in the printing process temporarily, in particular to physically support overhanging parts or portions of the printing object. After the 3D printing process is finished, the support material is removed, e.g. in a removal step.
Accurate color reproduction is important in many applications of 3D printing, especially for design-prototypes or 3D copies, where a texture-mapped 3D scan of an object is to be reproduced in a color-consistent way. However, existing 3D printers, in particular the aforementioned polyjet printers, use colored printing materials which are highly translucent. Such materials have high transmission and scattering properties, which effectively result either in blurring of color edges, or severe dot-gain if care is not taken to account for these properties. Thus, the organization of the printing materials within significant distance to the surface of the printing object, e.g. as much as a half a centimeter, can greatly affect the perceived color. It is therefore highly important to control material placement several layers of voxels beneath the surface, taking into account the transmission and scattering properties of the materials, greatly complicating the computational aspects of half-toning algorithms.
There is the technical problem of providing a method for 3D color printing and a 3D color printing device by which a quality of the printing object, especially the quality of a color reproduction, is improved, in particular (but not exclusively) if translucent printing materials are used. Further aspects are to provide a method for 3D color printing and a 3D color printing device which enlarge a color gamut of a 3D color printing device and/or which allow a fast computational and efficient processing of desired printing data, in particular a generation of control data for printing.